1. Field of the Invention
The present invention relates generally to a flight control system for airplanes and, more particularly, to a flight control system using engine thrust for emergency flight control of a multi-engine airplane.
2. Description of the Related Art
Aircraft flight control systems are extremely reliable. Multiple control surfaces, hydraulics, sensors, control computers, and control cables are used to achieve high levels of control system redundancy and reliability. However, during extremely rare occasions potentially disastrous flight control failures do occur. This is particularly true for military airplanes operated in a hostile environment. At such times, any other form of flight control would be welcome.
There are conventional backup control systems installed on many airplanes. Conventional backup control systems usually involve redundant control cables, redundant hydraulic systems, or redundant electronic control systems, and move the primary flight control surfaces, e.g., elevators, ailerons, rudders and flaps. Conventional backup control systems are vulnerable to damage which will render the flight control system useless, resulting in loss of the airplane. For example, on some airplanes, total loss of all hydraulic systems will cause loss of the airplane. In other airplanes, total loss of all control cables will cause the loss of the airplane. In still other airplanes, loss of a control surface, such as an elevator, will cause loss of the airplane.
It is well known that the flightpath of some aircraft with multiple engines may be controlled to a rudimentary degree by manually adjusting the throttle controls. Airplanes have flown with total hydraulic failures for substantial periods by manually adjusting the throttle controls. However, control was not sufficient for landing, resulting in a crash. This is because flightpath change in response to manually adjusting the throttle controls is very slow compared to that in response to normal flight control systems.
U.S. Pat. No. 3,146,972 to Engel, issued Sep. 1, 1964, discloses another type of conventional backup control system that uses auxiliary engines to control the flightpath of an aircraft. The auxiliary engines are arranged to supply thrust in various directions to overcome emergency conditions while the aircraft is in flight. The auxiliary engines are provided in addition to the main drive engines. Consequently, this type of conventional backup control system is expensive and involves modification of the aircraft to include the auxiliary engines.